The invention generally relates to systems in which signal amplitude sensing and/or waveform envelope extraction is needed.
Cochlear implants (or bionic ears) have been implanted in tens of thousands of people worldwide. Cochlear implants typically mimic the function of the ear by stimulating neurons in the cochlea in response to sound. FIG. I shows an overview of a common signal-processing chain that may be used in a cochlear implant. Only four channels of processing are shown although cochlear implants typically have 16 channels. Sound is first sensed by a microphone 10. Pre-emphasis filtering and automatic gain control (AGC) are then performed on the input at pre-emphasis filtering and AGC unit 12. Analog implementations of the AGC require envelope detection to be performed. Bandpass filters 14, 16, 18, 20 divide the AGC output into different frequency bands. Envelope Detectors 22, 24, 26, 28 then detect the envelope of the waveform in each channel. The dynamic range of each channel's envelope output is then compressed at compression units 30, 32, 34, 36 to fit into the electrode dynamic range via the nonlinear compression blocks. Finally, the signals from each channel are modulated at modulation units 38, 40, 42 44 by the compressed envelope information and sent to the electrodes to create charge-balanced current stimulation. Conventional cochlear implant systems typically employ a digital signal processor (DSP)—based system that may be worn as a pack on the belt or as a unit to be worn behind the ear.
There is a need, however, for a system and method that may be fully implanted. Reducing the power required for a cochlear implant would facilitate the development of a fully implanted system.